An orally administered pharmaceutical preparation passes through the esophagus and releases the contained drug while moving in the digestive tract. Since this digestive tract has a certain length, it will take a certain period for the pharmaceutical preparation to move along the tract, wherein the pH of digestive juice varies from acidic, weakly acidic to weakly basic. Some drug is metabolized in the digestive tract, while almost all drugs are metabolized more or less after they are absorbed into the body. In order to secure the desirable pharmaceutical effect with high safety, release of the drug from the pharmaceutical preparation should be precisely controlled. For this purpose, many techniques have been developed for the controlled release of drugs from oral pharmaceutical preparations (cf. "Iyakuhin no Kaihatsu, Yakubutsu Soutatsu-hou (Drug Delivery Method" Development of Medicine), Vol. 13, Hirokawa Shoten).
However, techniques used in the conventional pharmaceutical preparation for controlled release are mainly for the sustained release of the drug while it passes through the small intestine, the principal absorption site for many drugs. Therefore, these preparations, especially those for treating stomach disorders, cannot be expected to stay at a high concentration over a long period at the affected site.
There have been several reports on the endogastric residence of drugs. For example, a pharmaceutical preparation containing a drug and an additive to generate carbon dioxide gas, which enables the drug to float on the gastric juice utilizing the buoyancy of the generated gas in the stomach (Watanabe et al. Yakuzaigaku (Pharmaceutics), Vol. 153, No. 1, 1-7 (1993)), and a pharmaceutical preparation containing a drug and a viscous solution (e.g. an aqueous solution of sodium alginate), which can prolong the time of endogastric residence of the drug upon oral administration (Yasuhiko Tabata et al. Sustained-release of the cell growth factor in the biodegradable hydrogel using an intermolecular complex of macromolecules, the Pharmaceutical Society of Japan, the 118th Annual Assembly, Abstracts 31-TC-10-1, 1988) have been proposed. In addition, the development of a carrier for sustained release of drugs using a hydrogel of gelatin cross-linked with glutaraldehyde has been reported (Yasuhiko Tabata et al., Sustained release of the cell growth factor from biodegradable hydrogel using an intermolecular complex of macromolecules, the Pharmaceutical Society of Japan, the 118th Annual Assembly, Abstracts 31-TC-10-1, 1988). Including the above reports, no sustained-release agents comprising oil or polysaccharide have been hitherto reported.